Dry ice refrigerator



April 13, 1954 Filed March 3, 1952 R. L. KOCH 2,674,859

DRY ICE REFRIGERATOR '3 SheetsSheet l INVENTOR.

Robert L. Koch BY MW Q4 Affom R. L. KOCH DRY ICE REFRIGERATOR April 13, 1954 Filed March 3, 1952 3 Sheets-Sheet 2 INVENTOR: Robert L.Koch

April 13, 1954 R. KOCH DRY ICE REFRIGERATOR 3 Sheets-Sheet 3 Filed March 3, 1952 Patented Apr. 13, 1954 UNITED STATES PATENT OFFICE 4 Claims.

(Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes Without the payment of any royalty thereon.

This invention relates to apparatus and systems for cooling various materials using a refrigerant such as solidified carbon dioxide, or dry ice.

It is an important aim of the invention to present an apparatus of such nature that it may be readily manufactured at low cost so as to cocupy an extremely small amount of space, and yet will be effective in its intended function, to refrigerate a relatively large space.

It is also an important object to present such an apparatus with a circulatory system for a liquid secondary refrigerant which will operate effectively under conditions of severe physical shock, vibration, accelerated and ldecelerated translatory movements of the system.

Another object is to present such a system which may be so embodied as to be effective in varying positions of the apparatus, and varying inertia forces due to abrupt motions of the unit incident to transport thereof.

A highly important purpose of the invention is to offer a system of the extreme simplicity indicated, which will incorporate means to automatically control the rate of circulation of a liquid refrigerant in a heat exchange space, with out the use of thermostat devices or valves.

Additional objects, advantages, and features of the invention, reside in the construction, arrangement, and combination of par-ts involved in the embodiment of the invention, as will be understood, shown, or described in the following specification and accompanying drawings, where- Figure 1 is a vertical sectional view :of a simple embodiment of the invention suitable for use in small apparatus, as for instance for freezing cut oil vapors from high vacuum systems, and for .a portable unit including a cooled chamber in which a material to be kept .cool may be placed.

Figure 2 is a top view of a unit suitable for refrigerating a bottle;

Figure 3 is a vertical section of a modification of the apparatus;

Figure 4 is a similar view of a further modification;

Figure 5 is .a plan of-one of the cooling fins for the heat exchange loop.

There is illustrated in Figs. 1, 2 and .5, a freeze trap or heat exchange unit 1.0, which is ,a relatively small chamber arranged to he Ebrought etc extremely low temperatures for the purpose of rapidly chilling small objects, for instance to freeze out gas from vacuum systems, especially high vacuum equipment, as a means to facilitate the removal of air or other gas adhering to surfaces or otherwise retained in spaces from which it is to be removed.

The invention may, however, be embodied in large sizes and other shapes to adapt it to various uses, including the cooling of a, room or portable cabin; cooling electronic equipment cabinets, apparatus and cabins in supersonic airplanes, and cooling of motors in jet-operated motors and motors in guided missiles.

The trap In in the present instance is formally illustrated, without detail of the space for, and support means for objects, materials or articles to be chilled. A feature thought to be important for the trap is shown, however, consisting of a cylindrical flue H extending from bottom to top of the trap, and as shown open at top and bottom.

This may have means (not shown) for closing it at top and bottom, or for regulating the flow of chilled .air therethrough, or for conducting air from the flue to a more remote point for application to articles to be chilled; These details being discretionary and forming no novel feature of .the invention as to their structure, are not illustrated in detail.

The flue II is mounted beside or on an insulating case I2, which may be a box of conventional construction closed at the bottom and having a removable insulated charging cover l3 in its top part It. Spaced from the case walls within the case, a can or main container i5 is mounted, the upper flanged edge N5 of which may be attached to the top It, while its bottom I? is spaced above the bottom [8 of the case, the space under and around the can being packed with suitable insulation [-9. The cover it! may conform to the shape and size of the upper part of the can so as to form a closure for the can and permit charging of the latter with solid refrigerant such as dry ice, solid CO2.

A heat exchange loop 28, is shown symmetricah ly positioned within the flue l I. This may be a conventional coil on a normally vertical axis as illustrated, and in the present instance is shown as a single helical turn or convolution, one extremity of which is let into the wall of the can l5 near its bottom, extending outwardly from the can through the insulation 19 and wall of the case 12, and through the adjacent side of the flue H. The upper end of the loop is similarly let into the wall of the can .I 5 vertically above the lower end of the loop, and positioned a distance below the upper end of the can. The loop 26 is finned for better conduction of heat thereto, a number of these fins being of conventional washer form at 2|; while alternate ones 22 throughout the length of the 1001) are specially and perculiarly formed, to effect a major transfer of heat within the coil 2c; that is-acljacent the vertical axis of the flue H with which the loop is symmetrical. These special washers 22 are flat elongated blanks of sheet metal of good heat conducting characteristics, each having at one end a large aperture 23 adapted to fit snugly around the tube 2 3 of which the loop is formed as a continuous duct in one piece, although where required it may be segmented. The extended end of the fin is sufficiently long as at present illustrated to extend from the inner side of the loop tube 24 radially to the said vertical axis of the flue. part of the loop is of spiral form concentric with the flue axis, and its ends are extended radially outward from this axis so as to lie parallel to each other in the same radial plane of the flue axis.

The container and parts therein may be termed the refrigeration unit. Within the can l5 there is positioned a concentric inner central container 25 the wall of which is spaced sufilciently from the wall of the can if: to admit of intro duction of a charge of broken pieces of solid carbon dioxide between the two. The container 25 is also of a diameter to readily receive a quantity of similar lumps of carbon dioxide therein, as shown in Figure 1. The upper end of the container 25 stops at or slightly below the top end of the can l5, so that it will permit placement of the cover 13 without interference, and its upper end is open clear for introduction of the lumps of refrigerant readily. This end of the container 223 is closed by means of a stopper 2'5, which may be of cork snugly fitted in the container 25 so as to seal the upper end of this receptacle. It may have a lift or grip fitting 28 to be grasped or engaged by a tool for withdrawal of the stopper. The closure 13 may be secured in closed position releasably by snap buttons or spring catches 2t rounded so as to permit the cover to be forced to a snug fit in the charge opening through the top of the case. When so secured it lies closely over the stopper 28 so as to prevent the latter from being forced from the container 25 by gas pressure in the latter in normal operation of the apparatus. The cover I3 may be withdrawn manually, by moderate force sufilcient to press the spring catches 29 back from the path of the cover. A handle 30 is provided for lifting the cover from the charging hole.

The central container is provided with a plurality of radial fins 3i for conducting heat to the wall of the central container from a heat transfer liquid or secondary refrigerant in the can and loop.

An internal gas vent tube 32 is fixed within the central container, extending from near the stopper 21, where it is provided with a gooseneck 33, to the bottom of the container. Its lower end is extended longitudinally into the lower or infiuent end 34 of the heat exchange loop 26 toserve as a discharge nozzle for gas generated in the central container. The upper effluent end 35 of the heat exchange loop 20 is preferably connected to the can 15 a sufficient distance below the top of the latter to insure that when the can is filled with the secondary refrigerant liquid and lumps of dry solid refrigerant, .and

Th major after the latter becomes nearly exhausted, there will still be enough liquid in the loop and can to permit its ready circulation by flow from the can into the lower end of the loop and from the upper end of the loop back to the can.

In the cover i3 a vent tube or valve 38 may be provided, opening to the atmosphere, which may if desired include a pressure regulator so that a predetermined pressure will be maintained in the circulatory system. This could be utilized to regulate absorption of CO2 by the alcohol, if desired, or to limit evolution of gas from the solid C02.

The space 31 around the central container is filled with alcohol and lumps of carbon dioxide, and the central container is likewise filled with the same kind of liquid and solid lump refrigerant with the liquid level below the gooseneck Other liquids may be used if found desirable, as the secondary refrigerant, but alcohol is chosen because the carbon dioxide is solvent therein only to a limited extent (approximately 31 gr. per ml. at 15 C.) and the alcohol will not freeze at temperatures encountered in the operation of the system. Other liquids will serve this use, as for example, acetone, kerosine, or ether. Also, if extremely low temperatures are not required, or it is desired to conserve the CO2 in the container 15 or 25 the container i5 may be additionally packed in carbon dioxide snow at 19, the case wall l2 and bottom being formed of a light cellular wood adequately thick to serve as an insulation.

In the operation of the system as described, the containers being filled as described, a certain amount of CO2 given oif by the solid refrigerant will be absorbed by the alcohol, and the latter will be lowered in temperature to near that at which the solid refrigerant sublimates. Any excess of gas involved by this establishment of thermal equilibrium will be vented at 36.

An object to be chilled is placed in the space within the flue, and as heat is transferred from such object to the air in the space within the flue, the fins 2l-22 take up and conduct heat from the air to the tube 2i and the liquid secondary refrigerant in the tube. The resulting change in density of the liquid in the loop 20 causes it to rise and enter the outer main container l5, where it contacts the Dry Ice in the outer space 31 around the central container 25.

- Here, as the liquid starts to descend in the space 31, heat will be communicated to the Dry Ice lumps and to the fins 31 of the central container. The solid refrigerant in the space 31 will be caused to sublimate as the heat of vaporiza-' tion is communicated to the refrigerant. At the same time, the heat taken up by the fins 3! is communicated to the alcohol in the central container 25 and thus to the Dry Ice in the latter, causing evolution of some gas within the central container, but this will be at a lower rate per unit quantity of dry refrigerant than manifest in the main container l5, due to the fact that the rate of transfer of heat between two bodies in contact is proportional to the diiference' in temperature of the two, and the difference in temperature between the refrigerant in container l5 and container 25 will be less than the difference between the temperature of ambient air and the refrigerant in the loop, and the conduct of heat from the secondary refrigerant to the lump refrigerant in container [5 will normally be more efiicient than to container 25, due to direct contact between the liquid and.

lumps and to the greater. surface-exposure of solid refrigerant in "container 15, as well as the fact that the solid refrigerant in container l5 cools the loop liquid, and-cools the container 25.

Should the solid refrigerant not be promptly replenished in the container 15, however, the quantity in the container i5 will rapidly {diminish toward exhaustion, so that a greater relative activity in container 25 will follow, causing greater jet acceleration of flow in the loop, and by more efiicient convection and conduction more rapidly to container 25, accompanying increased absorption-in the latter. compensation for re duced absorption in the container is derived for a time. T a

The gas which is thus given off in bo'th 'ccntainers is itself at a low temperature and will absorb some heat from the circulating alcohol. Within the heat 'exchang'elo op there may be some evolution of gaseous C02 from the liquid secondary refrigerant due to the change in temperature of the latter, and'as the liquid is chilled in the main container it will absorb a corresponding amount of CO2 being evolved by sublimation of the solid CO2. Any gas released by rise of temperature of the liquid in the loop 2i! will aid in the circulation of the liquid refrigerant.

The gas evolved by sublimation of the solid refrigerant in container raises the pressure therein somewhat, and rises quickly to the upper part of the space therein, so that it escapes through the gooseneck 3'3 and vent tube 32. It is thus discharged into the lower "end "of the tube 20 with a jet action which impels the liquid along the tube, accelerating the movement thereof also by lessening the weight of the column, and by entraining action. Passage of the gas through tube 32 in the lower part of thecentral container insures its chilling to the lowest temperature in the refrigeration unit, either'aiding in cooling the liquid refrigerant or avoiding raising its temperature, and at the same time serving to absorb some heat communicated to the liquid in theloop 20 from air in the flue H.

This system can beutilized to produce temperatures in the neighborhood of or lower in the flue H, and may lower the temperature to or near the level of sublimation temperature, liquefaction of the solid CO2 being avoided as long as low pressures are maintained in the containers.

The possibility of operating the system by liquefaction of the solid CO2 and without material evolution of gas, by transfer to the solid refrigerant of the latent heat of fusion may be considered in conjunction with maintaining a sufficient pressure by the appropriate use of a regulating valve at the vent 36. This would avoid material change of weight of the unit during operation and also would obviate the emission of gas from the device.

In Figure 3, there is shown a system in which the apparatus may be identical with that described in Figure 1, but the solid refrigerant is omitted in the space 31 around the container 25', and the system operates entirely by absorption of heat by the solid refrigerant, in container 25', and sublimation of gas from the solid refrigerant in the central container with consequent absorption of heat by the gas released through the vent. The same reference numerals hereto fore applied are used on unchanged parts of Fig. 1, and parts modified are indicated by the same numerals with the addition of a prime. In this tainer [5, in case recharging of the central container with solid refrigerant frequently required. 7

Inthe case of Figure '2, the refrigeration occurs principally by transfer ofhe'at from the alcohol of the circulatory system to the alcohol in the central container and then to the solid CO2 therein; and by some absorption of heat from the loop liquid by the jet gas from the tube 32. The circulating alcohol will become saturated with CO2 after some operation, and the heat transfer at the loop may then continue by absorption in the alcohol from the wall of the tube '24 of heat brought to this wall through the fins 2i22 as before indicated, followed by transfer to the ebullient gas discharged from 'tube32, and transfer to the central tank and contents as before described.

The system of Figure 3 is suitable to use where a small amount of heat to be absorbed in the flue I i, or where lower temperatures are not re quired in the more extensive refrigeration of materials. I

In Figure 4 there is shown a further modification of the system in which the transfer loop and cooled space elements may 'be in accordance with the description of Figure l, but a greatly simplified construction of the refrigerator unit proper is disclosed. In this instance the container 45 corresponding to the outer container l5 of the first embodimentsof the invention is of similar height in relation to the heat transfer loop and the latter issimilarly connected to the receptacle, the influent end 34 of the loop being shown. The construction involves the further feature of a hood 46 secured to the wall of the container 4'5 over the opening or port 41 'of the lower end 34 of the heat exchange loop. This hood is inclined downwardly from the Wall of the container over the port and inwardly toward the center of the container 45, and may also be inclined slightly downwardly as at 48 in each direction laterally from the port 41. The far edge portion 49 of this hood may have a slightly increased downward inclination for a short distance, so as to better entrap gas evolved by solid refrigerant in the lower part of the container 45. The bottom 50 of this container may also be sloped from its distal side downwardly toward the port 41. This will result in some gravitation of the lump refrigerant toward the hood and small particles will be forced under the hood as diminution occurs, whereby asufilcient amount of gas freed in the bottom part of the container will be trapped by the hood and guided to the port 4! to percolate through the heat exchange loop and aid in the circulation of the liquid refrigerant. The movement will be orbital, as in the other forms of the invention, liquid rising through the loop 20 and descending through the container 45, the heat transfer and refrigeration in the latter being efiected substantially in the same way as in the container [5 of Figure 1.

When the device of Figure 4 is used in conjunction with the inner container shown in Figis desired to be less ure 1. the apparatus is capable of much mor rapid cooling of material positioned in the space within loop 20 or flue ll, due to the added acceleration of circulating liquid refrigerant, which results from displacement of liquid in the loop by gas bubbles from under the hood with a consequent liquid column in the loop which is much lighter than effected by the apparatus of Figure 1 alone; and also, by reason of rising motion of gas bubbles, which will more effectively entrain and propel liquid through the loop. While presence of gas bubbles in the body of liquid in the container will also have a somewhat similar effect, it is counteracted by local eddies and return movements of liquid in the container, whereas the gathering of bubbles by the hood and confinement of liquid in the loop produces a larger concentration of rising gas bubbles in the loop column as compared to the column in the tank.

It will be appreciated that the apparatus and system as disclosed is of such nature that it will not require a critical orienting with respect to the vertical, but will operate well when tilted considerably from the ideal vertical position.

It should be appreciated that, when an object has been chilled in the heat exchange to a low temperature, there will be a smaller amount of heat transferred and communicated to the refrigerator unit than when the object is first placed in the device, and there will be a reduced evolution of gas in the refrigerator unit. This will mean a reduced dissipation of the solid refrigerant and a reduction of the rate of how of the liquid secondary refrigerant. When the heat exchanger is kept closed for a considerable time, the temperature will be reduced in the whole system close to the critical one for sublimation of the solid refrigerant, expenditure of the latter will approach cessation, and flow of secondary refrigerant will approach a static condition.

I claim:

1. A refrigeration system comprising a container of primary solid sublimable refrigerant a heat exchange loop conduitexternally of said container having opposite ends in communication with said container said loop being ascendant from the lower part of said container from one end of the loop to the other end of the loop, a

liquid secondary refrigerant in the container and filling said loop and having a level thereabove in the container, a, solid sublimable refrigerant in the secondary refrigerant in the container, and hood means in the container at said one end of said loop projected into said container and spaced from the bottom of the container to trap and conduct to the lower end of said loop a portion of gas evolved by sublimation of said primary refrigerant, and means to vent gas from said main container.

2. The structure of claim 1 wherein the said means to trap gas comprises a hood fixed on the wall of said container over the lower communication of said loop with the container, and having surfaces extended inward from said wall and laterally of said lower communication of the loop with the container, and sloped upwardly from its distal parts toward said loop, said container having a bottom spaced from the extreme edge of the hood to admit a part of said solid refrigerant thereunder.

3. The structure of claim 2 in which said bottom of the container is sloped downwardly from distal parts of the container toward said end of the loop.

4. The structure of claim 1 in which a sealing stopper is fitted in the upper end of the central container, and a closure for the main container over and in retaining relation to the stopper, and releasable means to hold the closure in closing position on the main container, said closure being movable for opening in the direction of movement of said stopper.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re 19,055 Copeman Jan. 16, 1934 1,893,228 Copeman Jan. 3, 1933 1,989,247 Rooney Jan. 29, 1935 2,078,129 Du Bois Apr. 20, 1937 2,097,685 Bolton Nov. 2, 1937 2,122,381 Raymond June 28, 1938 2,244,904 Brown June 10, 1941 2,255,356 Harris Sept. 9, 1941 2,437,332 Newton Mar. 9, 1948 2,507,866 Plesset May 16, 1950 

